The multiple gun glitch on WAW was patched years ago on PC I think, in any case it doesn't exist on custom maps unless the mapper screwed up something.
Also I've been told that if a gun has it's own script (i.e. most wonder weapons) it's possible that it's precached before the weapons in the .gsc I showed you above, and as such would take priority (so less chance of losing it).

Correct. Assuming BO3 is the same, which I presume it is since I know I have lost guns that were not in my '3rd slot' several times. My friend attempted to rescript it (in WAW) so that it only takes your '3rd' weapon and I think he managed to, but it wasn't that easy and I think he had to alter a lot of other things to get it working. IDK why 3arc haven't done something like this but I'd assume it's just laziness as that is the policy they seem to take on a lot of things..

Lol I know what's in and not in WAW I've been modding it for nearly 2 years. I mean WAW but since the script is taken from BO1 it's the same thing basically. Mule Kick is hardly a difficult thing to port into WAW, it's just a 3rd inventory slot. Just like Staminup is 2 dvars, the engine in WAW and BO1 ZM is pretty much identical bar a couple missing functions and built in akimbo/D2P and slightly nicer lighting and whatnot. Anywho, the guns in a map are listed in a.gsc file and the order in which they are precached (read listed) defines their 'priority' when the engine decides which gun should be lost when downed with MK. For example, this is a snippet of my map's .gsc -
add_zombie_weapon( "weevil_zm", &"ZOMBIE_WEEVIL_1000", 1000, "", 0 );
add_zombie_weapon( "weevil_zm_upgraded", &"ZOMBIE_WEEVIL_1000", 1000, "", 0 );
add_zombie_weapon( "drakon_zm", &"ZOMBIE_DRAKON_1000", 1000, "", 0 );
add_zombie_weapon( "drakon_zm_upgraded", &"ZOMBIE_DRAKON_1000", 1000, "", 0 );
add_zombie_weapon( "xr2_zm", &"ZOMBIE_XR2_1000", 1000, "", 0 );
add_zombie_weapon( "xr2_zm_upgraded", &"ZOMBIE_XR2_1000", 1000, "", 0 );
In this scenario, if I had these 3 guns with MK and I went down, the XR2 would be taken first, regardless of whether it was in my first, second, or third gun slot, as it is 'below' the other 2 in the script. The Weevil would be the last one to be taken. Normally the starting pistol is the very first gun in this list so it is always taken last.
I'm almost positive that BO1/2/3 follow this same logic.

In WAW at least, the guns that you lose are taken by the order they are 'precached' in the scripts. So guns that are placed 'higher' up take priority. So the effect is it often feels like you are losing the 'wrong' gun. Not sure if they changed this logic for BO1/2, but I know I've lost the 'wrong' gun in BO3 before so I'd guess not.
As the starting pistol is usually precached first, you tend to keep hold of it when you lose your MK gun, this would also explain the scenario @83457 described above about the Wonder Weapon.

'Meatball' is not just the name coined by the community; that's the dev name for them (like the Apothican Servant's dev name is 'IDGUN'). R.A.P.S. are the multiplayer scorestreak that the meatballs are based off, but they are not supposed to be the same - why on Earth would the meatballs on Shadows of Evil go under the acronym 'Rolling Anti-Personnel Sentry'?? That makes no sense at all. The MP ones are robotic drones whilst the Shadows' ones are clearly supposed to be organic, semi-sentient beings.
Edit: On the wiki it says their 'official' name is 'Insanity Elementals' which I don't think is going to catch on somehow lol. It also says that Jack Vincent refers to them as 'meatballs', so all credit for this supposed 'crude' name should go to Treyarch.

The 'code' you are referring to was an fx called 'mech_flamethrower' or something similar I believe, which is one of the reasons why I think the Panzer is returning; as the Panzer's dev name is 'mech'. I'd love to see a next gen Panzer tbh, maybe throw in a few new moves and/or different weaponry (at one point in my map he had a minigun on his arm instead of a flamethrower for example) it would certainly suit the theme anyway.

He is a freelance mapper who currently maps for Treyarch, He mapped the Citadel Tunnels and some other areas in MOTD for BO2 (can be seen here if you are interested - https://www.youtube.com/watch?v=B3zY_tO0gFE) as well as some other MP/SP stuff, and they rehired him for BO3. He used to be a custom mapper for COD4 and WAW though (he actually mapped the spawn area in my map Oil Rig.) I spoke to him the other day and he told me he mapped the Waterfront district in Shadows of Evil, and there were 4 level designers (mappers) in total, and 22 members in the entire team who worked on the map overall.

Those puddles look to me to be just random decals/models that they have spammed around the map for detail. I can ask the guy who mapped the Waterfront district if you like and he can clarify what exactly they are, but I'm 99% sure they are nothing.

That would imply that there was not a way to upgrade it in the first place (or they removed it), which would be far worse. If they did add it in with a patch then I would be grateful that they made the right choice and obviously saw how desperately people were looking for it and decided to throw us a bone. If they didn't add it in with a patch and there isn't a way to upgrade it as is then that would piss me off a lot more.
But I believe that there is, and has always been, a legit way to upgrade it from day 1.

I agree that they fuck up a lot of things, and some of their 'patching' is questionable at best, and utterly baffling and incompetent at worst. But they would never intentionally have a legitimate 'step' of any EE that required the player/s to go down, that is just utter lunacy.